Double sampling dac and integrator

Electronic circuit components, such as resistors and active filters can be replaced by switched capacitor circuitry. Switched capacitor circuits allow tunable analog circuits to be manufactured with minimal use of resistors. Resistors may be difficult to integrate on silicon substrates, and can make the integrated circuit bulky. The switched capacitor circuits are typically used in order to integrate both analog and digital circuits on a single silicon chip. Switched-capacitor circuits can be used in digital to analog converters (DAC), analog to digital converters (ADC), instrumentation amplifiers, voltage-to-frequency converters, data converters, programmable capacitor arrays, balanced modulators, peak detectors, oscillators, and so on.

Main components of the switched capacitor circuits generally include switches, capacitors, and so on. The switched capacitor circuits employed in various types of ADCs, such as delta sigma ADCs, usually use a large number of capacitors and switches to realize the circuit. Ideally, the capacitance of the capacitors needs to be in a desired ratio, but may deviate from the desired ratio due to reasons, such as imperfections in the manufacturing processes and change of operating conditions (e.g., temperature, voltage, etc.). Such deviations are generally referred to as capacitor mismatch. Due to capacitor mismatches, a delta sigma ADC may not generate an accurate output. This may necessitate minimizing the number of capacitors in the circuit. In addition, switches in switched capacitor circuits may introduce noise in the circuit, and reduce the signal-to-noise ratio of the signal.

This disclosure relates to switched capacitor circuits, and particularly, to a single capacitor doubling sampling digital to analog converter (DAC) with reference loading independence. Reference loading independence is achieved by switching reference(s) to the same loading conditions (e.g., sampling capacitors with similar nominal values), independent from an input signal. The double sampling DAC and integrator circuit can be implemented in a variety of mixed signal circuits including analog to digital converters (ADCs), digital to analog converters (DACs), delta sigma modulators, etc. The following systems and methods are described with reference to a 1-bit delta sigma ADC; however, it is to be appreciated that the disclosed single capacitor double sampling DAC and integrator can be implemented in various other devices.

A delta sigma ADC is specific to a general group of delta sigma converters. A typical delta sigma ADC does not sample a complete input signal, but only the filtered difference between an input signal and a feedback signal. Therefore, fewer bits are required to sample the differences in the amplitudes, and preserving a desired signal to noise ration.

A delta sigma ADC is specific to a general group of delta sigma converters. Typically, delta sigma converters use over-sampling. Delta sigma converters can average multiple samples. These delta sigma converters are traditionally used for high-resolution low frequency (e.g., up to 1 MHz) applications, such as speech, audio, precise voltage, and temperature measurements. Delta sigma converters, such as a delta sigma ADC, can include a summing device, an integrator, a comparator, and DAC for converting a feedback signal into an analog signal for the summing device. Typically, these components are realized separately on a semiconductor substrate and require a large number of capacitors and switches to realize the integrated circuit.

The disclosed double sampling DAC and integrator circuit can replace the summing device, the DAC, and the integrator of the delta sigma ADC, thereby, reducing the total number of capacitor and switches required for realizing the delta sigma ADC. As fewer capacitors and switches are employed, the mismatch introduced in the circuitry due to the capacitors is reduced and the noise introduced by the switches is reduced. In addition, since the disclosed double sampling DAC and integrator combines the functionality of the summing device, DAC and integrator in a single circuit, the size of the delta sigma ADC can be reduced, thereby reducing its cost (i.e., manufacturing cost).